Why is It So Windy, Anyway?
2016-06-13 16:37:59.000 – Tim Greene, Intern
Mount Washington has already made national headlines a couple times this year on high wind days; this being because hurricane force winds have more or less been the norm for us this spring and so far this early summer. Normally in June we see an average wind of 27.6 mph, so far we are at 35.2 mph and have seen six days with gusts over 75 mph. So needless to say, the weather has been pretty intense lately. This is something I got to see firsthand when I was assigned the task of retrieving the precip can
(a glorified rain gauge) in hurricane force winds this morning. But I am only the most recent to experience the extreme winds inherent to Mount Washington. It all started (or better yet, was witnessed for the first time) just two years after the Observatory was founded, a world record wind gust of 231 miles per hour was observed on April 12, 1934.
Screenshot from the video of me going out to swap precip cans with winds gusting over 100 MPH
A frequent question we get asked at the Observatory is why is Mount Washington so windy? After all, as far as mountaintops go, 6,288 feet isn’t that tall; not even for America (Mount McKinley has a summit elevation of 20,320 feet). Mount Washington isn’t even the tallest peak in the Appalachian Mountains; North Carolina’s Mount Mitchell, at 6,684 feet boasts that claim. In fact, Mount Washington falls outside of the top ten tallest mountains east of the Mississippi River. So if it isn’t height, what is it? As it turns out, the extreme conditions are the result of a culmination of environmental factors that all serve to intensify weather patterns that converge on New England.
Low pressure systems, by way of their warm and cold fronts, transport air masses across the globe and thus create what we think of as “the weather.” A large number of these systems are steered through the northeastern corner of the United States by the jet stream, which is like a meandering river of fast-moving air tens of thousands of feet above the surface of the Earth. On average, every three days there is a front passing over New England, making the weather subject to frequent change. Situated in northern New Hampshire and the heart of northern New England, Mount Washington is in a perfect location to get repeatedly buffeted by weather patterns.
Thirty year average track over low pressure systems across the continental United States
Topography plays perhaps the largest role in making Mount Washington one of the windiest places on the planet. The Appalachians, which stretch from Georgia to southern Quebec, run roughly run southwest to northeast through North America. In New Hampshire, the portion of the Appalachians that run through the state make up the White Mountains, but there is a subtle feature that bucks the trend of the rest of the continental mountain chain. As you can see illustrated below, the Whites form a V-shape that funnels westerly (originating from the west) winds right over the summit of Mount Washington. Air is a fluid, meaning it shares its physical properties with liquids such as water. If you’ve ever put your finger over the end of a garden hose you have demonstrated the effects of Bernoulli’s Principle, which states that increasing the pressure of a flowing fluid will also increase its speed. This is what accounts for the strongest winds we see at Mount Washington being out of the west; the air is unimpeded for a span of over 1,500 miles at this altitude (you’d have to go as far west as the Black Hills of South Dakota to find anything above 6,288 feet). Additionally, the atmosphere has a natural “cap” that separates this layer of the atmosphere (the troposphere) from the next (the stratosphere) and thus constricts air even further, this time in the vertical direction.
Topographic map of the White Mountains
Annotated topographic map of the White Mountains
And so it is that all these conditions compounded make Mount Washington a sort of natural weather laboratory. Though it is uncommon to see winds gusting in excess of 100 mph in June, it certainly is not unheard of. As a matter of fact, in July of 1996 observers recorded a peak gust of 154 mph. So in spite of the recent notoriety Mount Washington is receiving of late, the only thing that’s new is the limelight.
Tim Greene, Intern